A CoCrPt-oxide granular type magnetic recording layer is presently used in a medium of an HDD, and CoCrPt magnetic grains must be downsized in order to increase the areal recording density. If the magnetic grains are downsized, however, the thermal stability decreases, and data easily disappears. The thermal stability can be increased by increasing the perpendicular magnetic anisotropy, but the coercive force in high-speed magnetization reversal also increases. If the coercive force becomes higher than the recording magnetic field of a head, it is no longer possible to perform satisfactory recording.
Although a BPM (Bit Patterned Medium) has been examined as a solution, the flatness of the medium surface worsens when patterning a magnetic recording layer, and this causes easy contact between a head and the medium. Accordingly, a medium having an unpatterned surface is favorable. Also, the servo and data bit positions of the BPM are determined when patterning the medium, but it is desirable to be able to freely set these positions after the medium is completed.
From the foregoing, a medium called a PPM (Percolated Perpendicular Medium) has been proposed. In the PPM, bits are maintained by pinning the domain walls by forming pores or nonmagnetic pinning sites in a domain wall motion type magnetic layer. The thermal stability is high because one bit surrounded by the domain walls is the unit of thermal decay, and domain wall motion decreases the coercive force, so easy recording can be expected. Experimentally, however, a CoPt-oxide-based PPM, for example, has the problem of an insufficient perpendicular magnetic anisotropy and the problem of heating, and a Co/Pt-pore type PPM, for example, has the problem of surface flatness because a substrate is processed.